Radio frequency (RF) communication systems have practical applications in the military, commercial aircraft industry, and telecommunication industry. Mechanically rotating antennas are utilized in a variety of radar systems, such as, aircraft surveillance systems, on board ships, and on land-mounted radar installations. Because an antenna rotates, and an RF transmitter does not, connectivity between the transmitter and the rotating antenna is critical to system performance. RF rotary couplers are commonly used to transfer the RF energy between the stationary and rotating components.
In order to build multichannel rotary couplers it may be necessary to stack individual channels on top of one another. To connect those channels from the stationary side to the rotating side of a parent multi-channel assembly, coaxial cables may be run up the axis of a rotary coupler. The stacked channels may have a through hole or channel down the middle of each module. Modules of this type are called “hollow shaft” or “around the mast” modules. For example, in order for the RF energy to be transmitted between the rotating and stationary sections of a rotary coupler, the energy may be fed onto a dynamic capacitive ring within a matched RF cavity (the dynamic capacitive ring is the section of the rotary joint that allows it to turn and also pass RF energy across the rotating section). Existing corporate feed assemblies used within hollow shaft modules are constructed radially, with the number of power feeds doubling with each additional circuit path. Thus, there is often a direct relationship between frequency, ring diameter, and the number of required coaxial feeds. The number of feeds that may be used to propagate RF energy to the dynamic capacitive ring increases with the diameter of the ring and the frequency. Thus, the diameter of the ring may be directly related to the size of the through-hole to pass ancillary cables from surrounding channels. For example, to construct a hollow shaft module with a through-hole or channel of 0.175 inch diameter that can carry an X-Band signal may include a 0.500 inch diameter capacitive ring. Feeding that ring may require eight individual feeds per ring (one rotor ring, one stator ring). Using existing design geometry, this may include three radially-placed power divider circuits to create eight feed paths, which, in turn, requires a relatively large housing diameter.
FIG. 1 is a schematic diagram illustrating a view of an example previous radio frequency rotary coupler 100. As described above, in order for RF energy to be transmitted between the rotating and stationary sections of a rotary coupler 100, the energy is often fed onto a dynamic capacitive ring. In prior approaches, corporate feed assemblies are constructed radially, with the number of power feeds doubling with each additional circuit path. In the example previous radio frequency rotary coupler of FIG. 1, the RF energy is fed from the stator 105 onto a dynamic capacitive ring 205 (FIG. 2) using eight coaxial power feeds 210a-210h (FIG. 2), and fed to the rotor 110 using a corresponding eight coaxial feeds 215a-215h (FIG. 2). Dividing the RF power from a stator input 115 to the eight stator feeds 210a-210h (FIG. 2) is accomplished on the stator side using a primary power divider/combiner 120, two secondary power dividers/combiners (not shown), and four tertiary power dividers/combiners (not shown). The RF energy is then passed across the dynamic capacitive ring 205 to the eight rotor feeds 215a-215h. On the rotor side, the power is then combined from the eight rotor feeds 215a-215h using four tertiary power dividers/combiners 135a-135d, two secondary power dividers/combiners 130a, 130b, and a primary power divider/combiner 125. The RF energy is then passed to the rotor feed 140. It should be understood that power can flow either from the stator side to the rotor side, or from the rotor side to the stator side. A given power divider/combiner acts either as a power divider or a power combiner depending on the direction of such energy flow, as should be understood by one of ordinary skill in the art. For the sake of convenience and readability, a power divider/combiner may be referred to herein simply as either a “power divider” or “power combiner.”
FIG. 2 is a schematic diagram illustrating another view of the example previous radio frequency rotary coupler 100 of FIG. 1. FIG. 2 provides a better view of the dynamic capacitive ring 205, the eight stator feeds 210a-210h, and the eight rotor feeds 215a-215h. 
FIG. 3 is a simplified schematic diagram illustrating one side of the example previous radio frequency rotary coupler 100 of FIG. 1. For a given side of the previous radio frequency rotary coupler 100 (either the stator 105 (FIGS. 1 & 2) or rotor 110 side), the power divider components can be schematically shown as in FIG. 3. For simplicity, FIG. 3 shows the rotor 110 side. The example rotor side includes a primary power divider 125, two secondary power dividers 130a, 130b, four tertiary power dividers 135a, 135b, 135c, and 135d, and eight rotor feeds 215a, 215b, 215c, 215d, 215e, 215f, 215g, and 215h, each coupled as shown using appropriate circuitry. As can be seen in FIG. 3, the amount of area needed on the dielectric support to accommodate the circuitry according to this design can be large.